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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>计算圆的面积和周长</title>
</head>
<body>
        <h1><a href="../default.html">返回主页</a></h1>
    <div>
        <p>圆的半径：<input id="r" type="text"></p>
        <p>圆的周长：<input id="cir" type="text"></p>
        <p>圆的面积：<input id="area" type="text"></p>
    </div>
    <script>
    var r = prompt("请输入圆的半径：");
    r = parseFloat(r) && Number(r);
    if(!isNaN(r)){
        var cir = 2*Math.PI*r;
        var area = Math.PI*r*r;
        document.getElementById('r').value = r;
        document.getElementById('cir').value = cir.toFixed(2);
        document.getElementById('area').value = area.toFixed(2);
    }
    else{  
        alert('请输入正确数字');
    }
    </script>
</body>
</html>